Application of palladium complexes bearing acyclic amino(hydrazido)carbene ligands as catalysts for copper-free Sonogashira cross-coupling

摘要

Metal-mediated coupling of one isocyanide in cis-[PdCl2(CNR1)(2)] (R-1 = C6H11 (Cy) 1, tBu 2, 2,6-Me2C6H3 (Xyl) 3, 2-Cl-6-MeC6H3 4) and various carbohydrazides (RCONHNH2)-C-2 [R-2 = Ph 5, 4-ClC6H4 6, 3-NO2C6H4 7, 4-NO2C6H4 8, 4-CH3C6H4 9, 3,4-(MeO)(2)C6H3 10, naphth-1-yl 11, fur-2-yl 12, 4-NO2C6H4CH2 13, Cy 14, 1-(4-fluoropheny1)-5-oxopyrrolidine-3-yl 15, (pyrrolidin-1-yl)C(O) 16, 3-(3,5-di-tert-butyl-4-hydrox yphenyl)propane-1-yl 17, EtNHC(O) 18] or sulfohydrazides (RSO2NHNH2)-S-3 [R-3 = Ph 19, 4-MeC6H4 20] led to a series of (hydrazido)(amino)carbene complexes cis-[PdCl2{(C) under bar (NHNHX)=N(H)R-1)(CNR1)1; X = COR2, SO2R3 (21-48, isolated yields 60-96%). All prepared species were characterized by elemental analyses (C, H, N), HR ESI+-MS, IR, H-1 and C-13{H-1} NMR spectroscopy, and by a single-crystal X-ray diffraction for 38. Complexes 21-48 demonstrated excellent activity as catalysts in copper-free Sonogashira coupling of aryl iodides and a variety of aromatic terminal alkynes. Catalytic system runs in environmentally benign EtOH ensuring product yields of up to 75-96% and TONs of up to 10(4). Mechanism of the copper-free Sonogashira catalytic cycle involving 21-48 as catalysts was proposed upon identification of key intermediates using HRESI-mass. (C) 2015 Elsevier Inc. All rights reserved.